This application is based upon and claims priority of Japanese Patent Applications No.2001-56009, filed in Feb. 28, 2001, the Contents being incorporated herein by reference.
1. Field of the Invention
The present invention relates to an optical wiring substrate utilized in information and communication systems that require high-speed and high-volume signal transmission, a method of manufacturing the optical wiring substrate and multilayer optical wiring.
2. Description of the Prior Art
In information and communication systems, optical signals suitable for high-speed and high-volume signal transmission are utilized. As for optical transmission between optical devices, optical fibers are utilized when the number of wires as optical wiring is small; meanwhile, when the number of wires is increased into several hundreds or thousands, an optical wiring substrate is utilized in which optical waveguides are provided on a substrate. Usually, a plurality of optical wiring substrates are laid, in which a plurality of optical waveguides are optically connected with each other for performing transmission of optical signals.
In this case, since light has high rectilinearity, alignment precision becomes an issue when optical fibers or optical waveguides on the substrate are coupled with each other. For example, a predetermined tolerance for misalignment between single mode optical fibers is about 5 xcexcm.
As for multimode optical fibers, a tolerance for misalignment between the optical fibers, each having a core diameter of several tens of micrometers, used for optical waveguides is within several tens percent of the core diameter.
There is also a case of coupling optical wiring substrates having optical waveguides formed thereon by use of a connector as another member. However, such a case may incur misalignment of 100 xcexcm or greater. Optical signals are not propagated when such misalignment greater than the applied core diameter occurs.
Moreover, in the case when light emitted from an optical waveguide of one optical wiring substrate is made incident on an optical waveguide of the other optical wiring substrate, it is desirable that the light is rendered parallel in optical path. There is a conventional constitution in which an end face of a core 1 is formed into a hemispherical shape as shown in FIG. 1, which is intended for rendering parallel light rays passes through the end face. Nevertheless, completely parallel light rays could not be obtained since the light reflected intricately within the optical waveguide.
Furthermore, coupling of hundreds or thousands of optical waveguides on optical wiring substrates may be contemplated by use of optical fiber connectors each fabricated with precision as a connector. However, the number of optical fibers allowable for such a connector is limited to a range from one to about twelve. Accordingly, an enormous number of optical fiber connectors are required for such use, which is unrealistic.
Since high-speed data transmission is enabled with optical signals, optical communications play a major role in long-distance transmission such as a backbone communication system. In particular, a technology of transmitting different kinds of information simultaneously with different wavelengths in one optical fiber is developed, which is called wavelength division multiplexing (WDM). High-volume information is thereby transmitted in a high speed.
At a relay station of a backbone communication system, the information sent by WDM is separated into light rays, each having a single wavelength. Then destinations of the individual light rays are switched, and the light rays are again coupled in one optical fiber.
In this case, a destination of the light ray of any wavelength needs to be switched arbitrarily. That is, a cross-connect function of changing inputs of N channels into outputs of N channels is required.
As the multiplexing of the WDM develops, it is estimated that 100 or more waves will be sent in one optical fiber. For this reason, the cross-connect function is required for a capability of processing 1,000 channels or more.
However, an optical switch capable of processing several thousands of channels does not yet exist. Accordingly, practically used are small switches arranged in a multistage combination, as shown in FIG. 2.
FIG. 2 illustrates a state that optical transmission between input optical fibers 410 and output optical fibers 460 is performed by channel processing of 64 channels of inputs and outputs with two sets of cross-connect wiring 430 using a three-staged configuration of a first switch 420, a second switch 440 and a third switch 450, wherein each switch has 8xc3x978 channels.
Each of the switches in respective stages includes a plurality of optical switches 470, each of which takes charge of a specific number of input optical fibers 410. In this case, the cross-connect optical wiring 430 must have an optical wiring structure in which wires between the switches of the respective stages are connected while intersecting one another.
Heretofore, Japanese Patent Laid-Open Hei 6 (1994)-331910 discloses a switching device for coated optical fibers that performs connection switching in arbitrary combinations.
However, a problem has been pointed out that the switching device requires a huge space for accommodating optical fibers in a case of 1,000 channels or more.
Accordingly, materialization of an optical wiring substrate that has a cross-connect structure capable of processing transmission of high-speed and high-volume data signals with 1,000 channels or more is anticipated.
Meanwhile, Japanese Patent Laid-Open Hei 11 (1999)-178018 discloses an optical connecting device of a structure in which a former stage substrate mounted with switches and a latter stage substrate are orthogonalized.
The optical connecting device simplifies wiring of the optical fibers therein. However, modes of mounting substrates are limited.
Moreover, in an optical cross-connect system in Japanese Patent Laid-Open Hei 10 (1998)-243424, a technology is disclosed for constituting a cross-connect structure in which a two-dimensional fiber array composed by laminating N fibers each of which has M cores and another two-dimensional fiber array having M fibersxc3x97N cores are orthogonally jointed.
Although a compact cross-connect structure is realized, the optical cross-connect system bore a manufacturing problem of an increase of coupling loss unless the lamination was exercisable in a cross-core pitch of optical fibers.
Moreover, there is also a method of using a fiber sheet technology, in which optical fiber strands are laid into arbitrary wiring and fixed in a sheet form with resin or the like. In this case, compact arrangement is feasible because the optical fibers do not have protection coating.
However, as previously shown in FIG. 2, the optical fibers are accumulated at the central portion of the intersection structure. Whereas a minimum bend radius is defined for the optical fiber, control of the bend radius in a vertical direction generated by lamination of the optical fibers becomes difficult. For this reason, there has been a problem that characteristics of the optical transmission may not be ensured by this method.
Recently, in the field of communications, the optical transmission is becoming a main stream not only for a long-distance signal transmission but also for a short-distance signal transmission. In conventional technologies of electrical signal transmission, clock frequencies and data transmission speeds are increased owing to progress in CPUs. Therefore, signal transmission speeds are improved day by day.
However, cross-connect devices that take charge of switching signals in the electrical signal transmission technologies are hardly applicable to signal switching for the optical communications without modification. Accordingly, optical via holes are particularly composed between layers of multilayer wiring, thus forming interlayer transfer portion of the optical signals. This interlayer transfer portion has a requirement that orientation of an optical signal therein does not change when an optical path is changed from one layer to another layer via the substrate.
Moreover, the optical via holes that take charge of switching the optical signals in the multilayer wiring of the optical communications had a risk of causing cracks by stress applied to the inside due to occurrence of air voids by reason of temperature changes during manufacturing processes thereof.
In addition, in the event that the light enters into the optical via hole from the optical waveguide, the light tends to spread in a progression direction due to wave nature of the light, and thus effective progression of the light in the optical path is impeded.
Moreover, conventional optical waveguides, which are constituted on an optical wiring substrate for transmitting signals and data in a device for information and communication systems that requires high-speed and high-volume signal transmission, are produced by a process of depositing a cladding material on a substrate such as a silicon wafer, followed by patterning core members.
In this case, there have been disadvantages such as cambers and cracks of the substrate caused by stress due to thermal hysteresis during the manufacturing steps of the optical waveguides.
Conventional technologies as countermeasures against such cambers and cracks have been insufficient for multilayer optical wiring substrates. For example, Japanese Patent Laid-Open Hei 8 (1996)-29632 is effective in a case of just one layer, however, removed portions of a cladding layer are buried in a multi-layered case. Such burying may be avoided by interpolating a film between layers in the event of multi-layering. However, a problem has been pointed out that stress would occur during a thermal process due to air thermal expansion of air layers remaining at slit portions.
Moreover, Japanese Patent Laid-Open Hei 5 (1993)-281424 is effective in a case of a ridge waveguide with just one layer. However, as for burying or multi-layering, a disadvantage of occurring cracks due to thermal expansion has been cited.
On the other hand, Japanese Patent Laid-Open Hei 6 (1994)-214128 requires deposition of stress layers on both sides of an optical waveguide layer thereof in the case of multi-layering in order to retain balance of the stress. Actually, this is not practical because of requiring multi-layering on both upper and lower faces of a substrate.
Moreover, as a conventional technology for forming a lens on a substrate, known is a manufacturing method of a micro lens as an optical element used for an optical pick-up device for reproducing information out of an optical memory. In Japanese Patent Laid-Open Sho 60 (1985)-155552, a planar micro lens is obtained by forming hemispheric hole portions by etching from two faces, filling a substance different from a substrate, and polishing the surface thereof. In Japanese Patent Laid-Open Hei 11 (1999)-177123, a constitution of disposing lenses on both faces of a substrate is disclosed.
However, alignment has been difficult in the event of forming the lenses on the both faces of the substrate.
For example, as shown in FIG. 3A, in conventional manufacturing steps of a micro lens used for an optical disk device or the like, in the event of forming concave portions 62 on both upper and lower faces of a substrate 61, and of forming lenses by filling the concave portions 62 with transparent substance 63 as shown in FIG. 3B, a disadvantage of a position shift 64 due to failure in accurate alignment of the upper and lower concave portions 62. Particularly such position shift becomes great when such manufacturing method is used for a large substrate, therefore it is hardly applicable.
In addition, since the substrate needs to be made of an optical material, it has been disadvantageous to form the micro lenses with a large substrate in terms of strength and costs.
Furthermore, regarding optical signal transmission in a device for information and communication systems that requires high-speed and high-volume signal transmission, optical connection of waveguides of optical wiring substrates requires alignment with high precision at connecting positions thereof, and is also emphasized in terms of enhancing a beam-condensing function thereof.
It is cited that collimating lenses and condenser lenses are required in order to optically connect the optical waveguides with each other. Conventionally known is a structure shown in FIG. 4, in which a spherical lens 87 is placed at a tip portion, of which light from a core 86 on cladding 85 is emitted out.
However, the spherical lens 87 has been required to align with the core 86 at high-precision. Accordingly, in the case where numerous optical waveguides are provided on the wiring substrates, each spherical lens needs to be provided corresponding to each of the optical waveguides. Moreover, in the alignment thereof, the center of the core 86 is aligned with the center of the spherical lens 87 with high precision of micrometric accuracy. For this reason, the structure resulted in disadvantages of high manufacturing costs as well as complex manufacturing steps.
Moreover, along with improvements in operational frequencies of the CPUs in devices for information and communication systems that require high-speed and high-volume signal transmission, improvements in clock frequencies and data transfer speeds are brought about.
Recently, high band technologies such as low voltage differential signaling (LVDS) and waveform shaping technology have been developed in order to improve transmission speeds. Although performance of electric transmission have been improved, transmission in a region at 10 Gbps or higher remains difficult because of occurrence of waveform distortion in the electric signals and the like.
In addition, in the long-distance transmission primarily composed of optical communications, an electric transmissive portion of a cross-connect device that performs path switching cannot fully bear optical communication speeds.
Consequently, technological developments took place in order to effectuate optical communications also in short-distance transmission, and a connecting mode between an optical transceiver module and an optical fiber has been materialized.
Moreover, an optical wiring substrate used for optical connections in short-distance and high-speed signal transmission is also known. For example, in a case of constituting multilayer optical wiring by laminating an optical waveguide layer in which a plurality of optical waveguides are arranged parallel to the x-axis direction and an optical waveguide layer in which a plurality of optical waveguides are arranged parallel to the y-axis direction, positions of optical connections between the layers are defined as shown in FIG. 5.
In an optical wiring substrate composed of an optical waveguide layer, in which a plurality of optical waveguides 91 are arranged on an optical substrate 90 parallel to the x-axis direction, laminated with a plurality of optical waveguides 92 arranged parallel to the y-axis direction so that they are orthogonal to the plurality of optical waveguides 91, interlayer optical propagation is performed by forming optical via holes at arbitrary intersecting positions 93 illustrated with shades in FIG. 5, selected from respective intersecting points of the plurality of the waveguides along the x-axis and those along the y-axis.
The optical waveguide layer shown in FIG. 8, composed by laminating the plurality of optical waveguides 91 arranged parallel to the x-axis direction and the plurality of optical waveguides 92 arranged parallel to the y-axis direction in order to intersect with one another, can be obtained by laminating an optical waveguide layer shown in FIG. 6 that includes the plurality of optical waveguides 91 arranged parallel to the x-axis direction with an optical waveguide layer shown in FIG. 7 that includes the plurality of optical waveguides 92 arranged parallel to the y-axis direction.
Register marks 94 are illustrated on each of the optical waveguide layers, and the multilayer optical wiring shown in FIG. 8 is obtained by lamination of optical waveguide layers based on the register marks 94.
In the multilayer optical wiring, an intersection structure of optical waveguides and a technique for interlayer connection of optical waveguides should be taken into consideration in order to effectuate wiring arrangements as in a conventional printed substrate.
In the case of laminating the optical waveguide layers, it is difficult to form the optical via holes, which are interlayer optical transfer portions, onto a substrate having a size of several tens of centimeters or greater for each side, with high accuracy of positioning of several micrometers or less by means of alignment using a conventional photolithographic technology.
Regarding the example of the conventional art shown in FIG. 5, in the case where two optical waveguide layers are laminated, the intersecting positions of the optical waveguides between the layers where the optical via holes are to be formed are indiscernible, because the waveguide layers are transparent. For this reason, lamination is performed based on the register marks 94, and intersecting positions of the patterned optical waveguides are determined as positions for the optical via holes, and laser processing is executed.
However, even if the optical waveguides layers are laminated based on the register marks, the positions for processing the optical via holes may be shifted because of position shifting of the waveguide pattern attributed to a mask for forming the waveguides or position shifting attributed to thermal hysteresis during the process of laminating the waveguides. Such disadvantages become a case of a large size substrate.
An object of the present invention is to provide an optical wiring substrate in which light emitted from an optical waveguide thereof is made as parallel light rays in an optical path, and multilayer optical wiring having an optical connection structure capable of jointing a pair of the optical waveguides without requiring accurate setting of the precision of jointing positions of the pair of the optical waveguides.
In order to achieve the foregoing object, an optical wiring substrate of the invention comprises a substrate, an optical waveguide being formed on the substrate and composed of a core and cladding, a slab optical waveguide and a planar convex lens continuously formed at tip portions of optical paths of the waveguides, mirrors for reflecting the light which transmitted through the convex lenses toward a direction intersecting a face of the substrate, and a lens in which the light reflected with the mirror is made as parallel light rays.
With the above-described constitution, in the optical wiring substrate of the invention, the light emitted from the core of the optical waveguide overpasses the slab optical waveguide and the planar convex lens, whereby a horizontal component of the light is rendered as parallel light rays. The light from the planar convex lens is reflected by the mirror and passes through a lens, whereby the light is rendered as the parallel light rays.
The light transmitted in the optical path is thereby rendered substantially parallel, thus it is accurately condensed into another waveguide jointed therewith via the lens.
Moreover, multilayer optical wiring of the invention comprises a first optical wiring substrate which includes a first substrate, a first optical waveguide being formed on the substrate and composed of a core and cladding, a first slab optical waveguide and a first planar convex lens continuously formed at a tip portion of an optical path of the first optical waveguide, a first mirror for reflecting the light which transmitted through the first planar convex lens toward a direction intersecting a face of the substrate, and a first lens in which the light reflected with the first mirror is made as parallel light rays, and a second optical wiring substrate which includes a second lens disposed opposite to the first lenses for allowing the parallel light rays from the first lenses to be made incident and condensed, a second substrate, a second mirror for reflecting the light which transmitted through the second lenses toward a direction parallel to a face of the second substrate, a second optical waveguide being formed on the second substrate and composed of a core and cladding, and a second planar convex lens and a slab optical waveguide continuously formed at a tip portion of an optical path of the second waveguide for allowing the light reflected with the second mirror to pass therethrough, whereby optical signals are connected between the first optical wiring substrate and the second optical wiring substrate.
With the above-described constitution, in a multilayer wiring substrate of the invention, the parallel light rays obtained from the first optical waveguide via the first slab optical waveguide, the first planar convex lens, the first mirror and the first lens are accurately condensed with the second mirror into the second waveguide. Accordingly, an optical connection between the first and the second waveguides is performed without being bothered by alignment of the waveguides.
In addition, another object of the present invention is to provide an optical wiring substrate having an effective multi-channel cross-connect structure in which input optical wiring and output optical wiring with n channels are laid out on two upper and lower layers without dependence on the number of the channels, and are connected one by one to each other across the different layers at each interlayer transfer position.
In order to achieve the foregoing object, an optical wiring substrate of the invention comprises a substrate, a plurality of optical wiring of an input side having N pieces of input terminals laminated on one face of the substrate, and a plurality of optical wiring of an output side having N pieces of output terminals laminated on the other side of the substrate and orthogonalized with the N pieces of the input terminals on the substrate, wherein the plurality of optical wiring of the input side and the plurality of optical wiring of the output side are connected one by one to each other across the different layers at each interlayer transfer position.
With the above-described constitution, in the optical wiring substrate of the invention, a linear portion of the input optical wiring and a linear portion of the output optical wiring are disposed on separate layers, and interlayer transfer takes place at a flexion of the input optical wiring and the output optical wiring.
N-channel inputs are thereby exchanged into n-channel outputs without dependence on the number of the channels, which is also readily applicable to a case where a large-scale cross-connect function is required.
In addition, another object of the present invention is to provide a method of manufacturing an optical wiring substrate having the steps of manufacturing optical waveguides thereof by forming an under cladding layer, a core and an over cladding layer, respectively on both upper and lower faces of a substrate, which includes a step of forming an incline of approximately 45xc2x0 as an optical via hole which reaches from the over cladding layer to the substrate.
In order to achieve the foregoing object, the method of manufacturing an optical wiring substrate of the invention comprises the steps of forming an under cladding layer on a substrate, forming a core layer on the under cladding layer, forming an optical waveguide pattern layer on the core layer, forming a core pattern as an optical waveguide by etching with the optical waveguide pattern layer as a mask, forming an over cladding layer after the core pattern is exposed by removing the optical waveguide pattern layer, forming an incline of approximately 45xc2x0 as an optical via hole which reaches from the over cladding layer to the substrate, and forming a reflective film on the incline of approximately 45xc2x0.
With the above-described constitution, according to the method of manufacturing an optical wiring substrate of the present invention, the optical waveguide as optical wiring which has the incline of approximately 45xc2x0 as the optical via hole can be readily manufactured on the substrate.
In addition, another object of the present invention is to provide an optical wiring substrate having manufacturing processes of optical via holes which take charge of cross-connect functions for switching optical signals in multilayer wiring of optical communications, capable of preventing cracks incurred by stress being applied inward due to air voids generated inside by temperature changes, enhancing focal power of light inside the optical via holes, and enhancing accuracy of a direction of light.
In order to achieve the foregoing object, an optical wiring substrate of the invention comprises a substrate, optical waveguides having different optical wiring layers on upper and lower faces of the substrate, optical via holes which connect the optical wiring layers, and a communicative portion which communicates the inside of the optical via holes with the outside.
With the above-described constitution, in the multilayer optical wiring substrate of the invention, light inducted into the optical via hole is condensed at an optical condenser, whereby the light inside the optical via hole is prevented from spreading due to the wave nature possessed by the light, thus reducing light loss.
In addition, another object of the present invention is to provide an optical wiring substrate, a multilayer optical wiring substrate and a method of manufacturing an optical wiring substrate, which are capable of avoiding occurrence of cambers and crack due to stress.
In order to achieve the foregoing object, an optical wiring substrate of the invention comprises a substrate, optical waveguides being formed on the substrate and composed of an under cladding layer, a core layer and an upper cladding layer, a pair of slits arranged substantially in parallel on both sides of the core layer, and at least one groove provided on the upper cladding layer for connecting the pair of slits.
Moreover, a multilayer optical wiring substrate of the invention comprises a substrate, a first optical wiring layer including optical waveguides being formed on the substrate and composed of an under cladding layer, a core layer and an upper cladding layer, a pair of slits arranged substantially in parallel on both sides of the core layer, and at least one groove provided on the upper cladding layer for connecting the pair of slits, and a second optical wiring layer of the same constitution as the first optical wiring layer, which is laminated on the first optical wiring layer and including at least a pair of slits, each slit communicating with one of the pair of the slits of the first optical wiring layer via the groove.
Moreover, a method of manufacturing an optical wiring substrate of the invention comprises the steps of forming an under cladding layer on a substrate, forming a core layer on the under cladding layer, forming a core pattern as optical waveguides by etching with an optical waveguide pattern layer formed on the core layer as a mask, forming an upper cladding layer after the core pattern is exposed by removing the optical waveguide pattern layer, forming a pair of slits substantially in parallel on both sides of the core layer so that the slits reach a surface of the substrate, and forming at least one groove on the upper cladding layer, which communicates with the pair of slits.
With the above-described constitution, the method of manufacturing an optical wiring substrate of the invention forms the pair of slits, which are substantially in parallel on the both sides of the core layer in the longitudinal direction thereof as to sever a plurality of the optical waveguide layers on the substrate, and the groove which communicates with the pair of slits, with an excimer laser. Accordingly, communication with outside air becomes feasible with the groove, thus relaxing stress incurred by volume changes with thermal expansion of air trapped in the respective slit portions of the layers especially in the case of multi-layering optical waveguides.
An optical wiring substrate of a multilayer constitution obtained by the above-described method of manufacturing an optical wiring substrate does not incur cambers or cracks.
In addition, another object of the present invention is to provide an optical wiring substrate and a method of manufacturing an optical wiring substrate, applicable to a large-size substrate without obstacles, upon propagation of light from one layer on a substrate to another layer thereon by performing accurate alignment of a pair of lenses provided on an optical interlayer transfer portion on the substrate.
In order to achieve the foregoing object, an optical wiring substrate of the invention comprises a substrate, an optical waveguide layer being formed on one face of the substrate, a photo acceptance portion being formed on the other face of the substrate, and an optical interlayer transfer portion provided on the substrate for switching optical paths from the one face to the other face, the interlayer transfer portion being composed of a through hole being formed on the substrate, and a lens being formed on at least one face of the substrate formed by layering two kinds of transparent substances each different in refractive index, which are filled in the through hole.
Moreover, a method of manufacturing an optical wiring substrate of the present invention comprises the steps of providing a through hole on a substrate, filling a first transparent substance having a specific refractive index in the through hole, forming concave faces respectively on both surfaces of the first transparent substance by polishing, and filling a second transparent substance having a refractive index higher than a refractive index of the first transparent substance in each of the both concave faces.
With the above-described constitution, according to the optical wiring substrate and the method of manufacturing the optical wiring substrate of the present invention, accurate alignment of lenses being formed on the both sides of the substrate becomes feasible, whereby a large amount of optical via holes and optical interlayer transfer portions which are optical interfaces, can be easily formed so that they are also readily applicable to a large-size substrate.
In addition, another object of the present invention is to provide an optical wiring substrate having a condenser function with easy aligning capability upon connecting a pair of optical waveguides of optical wiring and effective in the event of propagating light from one optical waveguide to another optical waveguide, which is particularly effective in the event of optically connecting a pair of opposed optical waveguides in a case where a plurality of optical waveguides are arranged.
In order to achieve the foregoing object, an optical wiring substrate of the present invention comprises an optical waveguide composed of a core of which a tip portion is formed into a convex shape and cladding contacting with the core and having a refractive index different from a refractive index of the core, the optical waveguide being supported on a substrate, and a cylindrical lens disposed opposite to the convex tip portion such that the center of the core coincides with the center of curvature of the cylindrical lens.
Moreover, an optical wiring substrate of the present invention has an optical connection structure for signals comprising a first optical waveguide composed of a core and cladding which has a refractive index different from a refractive index of the core and covers around the core, the first optical waveguide being supported on a substrate in a state that a tip portion of the core is exposed to air from the cladding, and a second optical waveguide composed of a core which has a tip portion exposed to air and is disposed in a position opposite to the tip portion of the first optical waveguide, and cladding which has a refractive index different from a refractive index of the core and covers around the core, the second optical waveguide being supported on a substrate for performing propagation of optical signals with the first optical waveguide.
These optical wiring substrates of the present invention have a condenser function with easy aligning capability upon connecting a pair of optical waveguides of optical wiring and effective in the event of propagating light from one optical waveguide to another optical waveguide. The optical wiring substrate can be obtained which is particularly effective in the event of optically connecting a pair of opposed optical waveguides in a case where a plurality of optical waveguides are arranged.
In addition, another object of the present invention is to provide a multilayer optical wiring substrate capable of confirming intersecting positions between layered optical waveguides with high precision, processing optical via holes, and reducing light loss upon connection of interlayer optical waveguides and dispersion of losses among channels.
In order to achieve the foregoing object, an optical wiring substrate of the present invention forms optical transmittance distributive regions axisymmetrically in a width direction of an optical waveguide layer which is composed of cores and cladding which has a refractive index different from a refractive index of the cores and covers around the cores.
Moreover, a multilayer optical wiring substrate of the invention comprises a first optical waveguide layer including a plurality of first optical waveguides parallelly arranged along an x axis, each of the first optical waveguides being composed of a first core and first cladding, and a first optical absorber with low optical transmittance arranged on both sides of the first optical waveguide axisymmetrically with respect to an axial center of the first core, and a second optical waveguide layer to be laminated on the first optical waveguide layer including second optical waveguides in parallel arranged along a y axis and arranged orthogonally with respect to the first optical waveguides of the first optical waveguide layer, each of the second optical waveguides being composed of a second core and second cladding, and a second optical absorber with low optical transmittance arranged on both sides of the second optical waveguide axisymmetrically with respect to an axial center of the second core.
With the above-described constitutions, the optical wiring substrate and the multilayer optical wiring substrate of the invention effectuate image recognition of intersecting positions by rendering optical transmittance in the intersecting positions of the optical waveguides higher than optical transmittance of other portions when viewed perpendicularly with respect to a face of an optical waveguide substrate. As a result, a plurality of intersecting positions between the optical waveguides can be detected individually and directly. And by determining the intersecting points as positions for forming optical via holes, processing of the optical via holes becomes feasible with less position shifts, which is of higher precision than a patterning process.
Moreover, a method of manufacturing an optical wiring substrate of the invention comprises the steps of forming a first cladding layer on a substrate, forming core portions by exposure treatment via a mask after forming a core layer on the cladding layer, forming a second cladding layer for covering the core portions, forming a third cladding layer on the second cladding layer with a substance having high optical absorptance, forming optical transmittance distributive regions axisymmetrically with respect to the cores after planarizing the third cladding layer.
With the above-described constitution, according to the method of manufacturing an optical wiring substrate of the present invention, optical absorbers can be formed between optical waveguides, whereby central positions of the optical waveguides can be recognized by a difference of optical transmittance of the optical absorbers.